The Neanderthal medicine cabinet was stocked with pain-killers and antibiotics.

Dental plaque, the bacteria-rich tooth film your dentist nags you about, is not usually seen in a positive light. But for scientists studying Neanderthals, humanity's closest extinct relatives, prehistoric plaque can be a godsend.

Much like the tree resin that traps ancient ecosystems in amber, plaque can preserve microbial lifeforms that proliferated in the mouths of our Neanderthal cousins, with whom early humans occasionally interbred before the mysterious species died out roughly 40,000 years ago. Hardened tartar and plaque, which is called "dental calculus," can yield a huge range of useful insights about the diet, lifestyle, and environment of Neanderthal communities, according to new research published Wednesday in Nature.

The study's authors, led by University of Adelaide paleomicrobiologist Laura Weyrich, showed that the Neanderthal diet varied enormously by region, from a meat-rich menu in Spy Cave, Belgium, to a vegetarian buffet in Spain's El Sidrón cave system. The team also identified a Neanderthal individual who was likely self-medicating with ancient painkillers and antibiotics, and whose mouth contains the earliest example of a microbial draft genome ever identified.

Weyrich and her colleagues were able to reconstruct all these fascinating details by extracting microbial DNA from the dental calculus of the Belgian and Spanish Neanderthal groups. The Belgian gang's teeth turned up microbial signatures of woolly rhinoceroses, wild sheep, and gray shag mushrooms, which have long stems and pleated caps.

These findings are in line with previously discovered bones of woolly rhinos, reindeer, mammoth, and horses in Spy Cave. These animals that may have been preyed upon by Neanderthals, who then stashed the remains inside their cave dwelling.

The dozen-odd Spanish Neanderthals, in contrast, subsisted on split gill mushrooms, which cluster together in close groups, normally on rotting wood, and have very short stems relative to the gray shag mushrooms. Pine nuts, forest moss, and poplar tree bark were also on the El Sidrón menu. Not much is known about these Spanish cave residents, who lived about 48,000-49,000 years ago, so the discovery that they had a primarily meat-free diet fills an important gap in our knowledge of their lifestyle.

"There is very little contextual information for the El Sidrón Neanderthals," Weyrich told me over email. "That is one of the great things about this new approach—we can learn cultural and dietary information about ancient hominids that we otherwise know almost nothing about!" The findings suggest that Neanderthals could readily adapt to different environments, and weren't necessarily reliant on meat consumption to survive.

Interestingly, the dental calculus of the best-preserved Spanish specimen, known as El Sidrón 1, also revealed evidence of self-medication. This particular individual was suffering from a chronic tooth abscess and a stomach bug called Enterocytozoon bieneusi, which likely caused diarrhea, among other possible symptoms. Weyrich's team used calculus samples to show that the Neanderthal chewed on poplar bark, which contains salicylic acid, an important ingredient in the painkiller aspirin.

The researchers also detected remnants of the mould Penicillium, which is used to produce the antibiotic penicillin. These are fairly sophisticated treatments for the Upper Paleolithic period, and suggest that Neanderthals were well aware of the medicinal properties of certain ingredients available in their habitat.

El Sidrón 1's dirty teeth led to another major discovery—the oldest draft microbial genome ever sequenced, belonging to the microbe Methanobrevibacter oralis. This microbe is often a sign of gum disease, and it was so well-preserved in the specimen that nearly the entire genome could be reconstructed by Weyrich and her colleagues. (The researchers can't say for sure whether or not the Neanderthal suffered from gingivitis, though M. oralis is associated with the condition.)

"This is the oldest genome to date by about 43,000 years, so it really is leaps and bounds older than any microbe that's previously been examined," she told me. This early genetic snapshot of helps clarify the timeline of pathogen exchange between humans and Neanderthals, and provides a benchmark for understanding how the hominid microbiome has evolved over the ages. To that end, Weyrich is working to expand the dataset of ancient dental plaque across several human relatives, to mine all the juicy information it contains.

"We would love to analyze other species of ancient hominids," she said. "We're also busy working on analyzing ancient dental calculus from thousands of ancient humans, trying to reconstruct ancient lifestyles and disease around the world over the past 20,000 years. We'll have lots of stories to tell, or rather, our ancestors will have lots of stories to tell us—I'm sure!"